The camshaft was another area where significant development contributed to the success of the engine combination. Chris elaborated: “I was aiming at a target rpm for peak power. We started off with a 246/252 duration [at .050], and it peaked at a certain rpm. We adjusted down, dropping to 238/244, and it was still peaking higher than desired. We finally went down to 228/234, and that peaked at 6,200 rpm with a carb. It helped the bottom end, and didn’t hurt the top end in the rpm range we were targeting.” The same process of zeroing in on the ideal specification through experimentation and testing was applied to the lobe separation angle. Chris expanded: “We started out in the 106-degree range, and then brought it down to the 102-104 range. The more we advanced it, the better the power curve. When we advance the cam and it improves, it might mean the cam is too big to start with, or it needs to be on a tighter lobe separation. We were zeroing in on both the duration and lobe separation at same time. To complement the fast-acting solid-roller cam, SAM used top-quality components in the valvetrain, including Manley springs and Jesel shaft-mounted rockers.
Another component that received extensive testing was the header. Here testing included everything from a “tri-Y” setup, differing lengths in the primary tubes, and several collector types. In terms of spotting trends, Chris tells us the changes were subtle: “The individual changes were so small that you would just look at the graphs and see where the power curve was affected, and then check the bottom line average power numbers. Often, the generally accepted theories did not pan out. For instance, we found a shorter primary made more power all the way down to 2,500 rpm, so we shortened them up. The primary tube size we used was 1⅞ inches all the way down to a 3-inch collector. On the collectors, the merge made more power everywhere than the open collector, and here the choke point of the collector proved to be a critical area.”
To The Competition
Much of the testing and subsequent modifications that went into developing this engine were prepared for the 2010 AMSOIL Engine Masters Challenge, however the team withdrew without running due to a failure of the oiling system. The oil pump would not prime to build pressure while cranking, and the team decided it wasn’t worth risking the possibility of destroying the engine. A chance for a reprieve came in the 2011 event, where the engine was mildly reworked to meet the rules, with the previous discussed combination. The SAM’s outstanding engine-building effort was validated as soon as the engine worked through its first set of qualifying pulls in the Street Division, taking First Place in qualifying, developing as much as 686 peak horsepower in the process. The point was driven home as the engine completed final eliminations to secure the Division Championship in Street. The success of the SAM engine in competition proves that building competitive horsepower is truly an ongoing process of development.